In hydrocarbon exploration and production there is a need to determine the approximate composition of oil samples in order to investigate their origin and properties. The production system of a developed hydrocarbon reservoir typically includes pipelines which combine the flow of several sources. These sources can be for example several wells or several producing zones within a single well. It is a challenge in the oilfield industry to back allocate the contributions of each source from a downstream point of measurement at which the flow is already commingled.
It is known to analyze oil samples to determine the approximate composition thereof and, more particularly, to obtain a pattern that reflects the composition of a sample known in the art as fingerprinting. Such geochemical fingerprinting techniques have been used for allocating commingled production from multilayered reservoirs.
There are many known methods of fingerprinting. Most of these methods are based on using a physicochemical method such as gas chromatography (GC), mass spectroscopy or nuclear magnetic resonance or others to identify individual components of a complex hydrocarbon mixture and their relative mass. In some known applications, a combination of gas chromatography and mass spectroscopy (GC-MS) is used to detect spectra characteristic of individual components of the complex hydrocarbon mixture.
Most fingerprinting techniques known in the art are based on the identification and quantification of a limited number of selected components which act as marker molecules. One such method is described in U.S. Pat. No. 5,602,755A to Ashe et al., and in the published international patent application WO 2005075972. Further methods of using compositional analysis for the purpose of back allocating well production is described for example in the U.S. Pat. No. 6,944,563 to Melbø et al.
Typically the produced fluids, if composed of reservoir effluent, such as mixtures of oil, gas and water contain many different chemical components or molecular species. Thus the number of potential geomarkers may range from several hundreds to thousands. However, among those there are often some markers which provide better accuracy in allocating production than others.
In the field of well testing it has been long known to measure the inflow performance relationship (IPR) between production or flow rate and the downhole pressure. A method of using the IPR to optimize production is for example demonstrated in the U.S. Pat. No. 4,442,710 to Meng. Its use for investigating multilayered reservoirs is for example described in the U.S. Pat. No. 4,803,873 to Ehlig-Economides. The measurement of flow rates and pressures from multilayered reservoirs is also described in the more recent co-owned U.S. Pat. No. 7,089,167 to Poe. Other known methods of determining IPRs and their use in multilayered reservoirs are presented in the Society of Petroleum Engineers (SPE) papers no. 10209, 20057, 48865 and 62917.
In the light of the known methods it is seen as an object of the present invention to provide a method of ranking components in commingled flow, in particular such that markers that could provide the most accurate measurement for back allocating flow are identified.